A medical technician accused of infecting at least 30 patients at a New Hampshire hospital with hepatitis C also worked in the past five years at hospitals in New York, Michigan, Arizona, Georgia, and Maryland, health officials in those states said Friday.

A day after federal prosecutors in Concord, N.H., charged David ­Matthew Kwiatkowski, state and federal investigators worked to ­determine whether the 32-year-old former Exeter Hospital employee, referred to by US Attorney John ­Kacavas as a “serial infector,” may have exposed other patients around the country to the virus, which can cause serious liver damage.

Dr. José Montero, New Hampshire’s public health director, said there is a “high possibility” of other infections. “We still don’t know the full magnitude of this,” he said.

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Kwiatkowski worked in so many states because he was placed in hospitals across the country by a health care staffing agency.

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Attorney Alfred Catalfo III of ­Dover, N.H., who represents 10 ­infected patients, said Kwiatkowski first was contracted to work at ­Exeter Hospital by Triage Staffing, a company based in Nebraska. The company did not return phone calls seeking comment. Catalfo said he is amending a negligence complaint against Exeter Hospital to include Triage.

The allegations “demonstrate a shocking level of negligence and lack of due diligence,” he said. “There were red flags all over the place that were ignored.”

Kwiatkowski is accused of taking syringes of Fentanyl, a powerful ­anesthetic, from Exeter’s cardiac catheterization lab, injecting himself, and returning dirty needles to treatment areas where they were used on patients. He had worked at the heart center for just over a year, ending in May.

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Exeter Hospital offered its most vigorous defense to date in a statement posted Friday on its website.

He was “an extremely good cardiac technologist who pulled the wool over everyone’s eyes,” Wharton said in the statement.

The hospital said Kwiatkowski provided “plausible explanations” to explain unusual behavior that ­investigators said was characteristic of someone using drugs.

Kwiatkowski once said his bloodshot eyes were the result of mourning a deceased aunt, though his parents later said there had been no death in the family, a federal affidavit said.

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“David had stories for everything that pulled at your heart strings, and we had no reason to disbelieve him,” Wharton said.

‘In this case, a primary problem was the lack of controlling access.’

The hospital hired Kwiatkowski as a full-time employee in October and performed a state criminal background check and a health evaluation, the statement said. Such exams would not typically include a test for hepatitis, according to state health regulators.

Investigators believe Kwiatkowski, whose certification through the American Registry of Radiologic Technicians expired this month, has been infected with the virus since at least June 2010. He has been charged with obtaining controlled substances by fraud and tampering with a consumer product. If convicted, he could face a 20-year sentence.

The New York State Department of Health alerted hospitals and radiology facilities Friday about Kwiatkowski’s alleged drug diversion,and urged them to review their personnel files to determine whether he had worked there. “If people visited a hospital when he was there, we want them to know,” said Bill Schwarz, a health department spokesman.

St. Francis Hospital in Poughkeepsie confirmed that Kwiatkowski had worked in the cardiac lab there for about three months ending in early 2008.

He then moved to Maryland, where he worked at the Baltimore VA Medical Center from May 2008 to November 2008, Southern Maryland Hospital from December 2008 to February 2009, Johns Hopkins Hospital from July 2009 to January 2010, and Maryland General Hospital from January 2010 to March 2010.

A statement from Johns Hopkins said there were no unusual groupings of hepatitis C infections during the time that Kwiatkowski worked there but an investigation is ongoing. About 200 patients may have had procedures in the facility where Kwiatkowksi worked, the hospital said. It is setting up a toll-free number and contacting patients directly to offer free hepatitis C testing.

Health officials in Arizona, Georgia, and Michigan, where Kwiatkowksi grew up, could not immediately provide details.

The cases raise questions about the use of unlicensed hospital workers. Nurses and doctors, not to mention barbers and tattoo artists, are typically licensed and regulated by state boards charged with disciplining professionals when appropriate, including in cases of drug abuse, and sometimes communicating with boards in other states.

While some states license certain categories of medical technicians, including some in radiology, many of these workers receive no oversight from state agencies.

Kwiatkowski was caught stealing narcotics from a hospital in another state, according to the federal affidavit. A hospital employee saw him swipe a syringe from an operating room. Three empty Fentanyl syringes were found on him during a search, the court records say.

“We are talking about somebody who may have been doing drugs in several different states and was still allowed to be in the system,” Montero said.

The question of whether medical technicians should be licensed is a valid one, said Dr. Sidney Wolfe, ­director of the health research group at Public Citizen, a consumer group. But, he said, the more pressing questions is, “Who was watching the Fentanyl cabinet?”

The US Drug Enforcement Administration has strict regulations requiring its hospitals to store powerful prescription medications — particularly Fentanyl, a Schedule 2 drug — in locked areas and monitor these substances as they are being prepared to be administered to a ­patient.

“In this case, a primary problem was the lack of controlling access,” Wolfe said.

The Centers for Disease Control and Prevention has documented three other cases since 2004 in which health workers have infected patients with hepatitis C by stealing drugs and leaving dirty needles ­behind for use on patients. Those cases have typically been talked about as isolated incidents. But, Perz said, “It’s getting harder for the health care community to make that argument.”

Patricia Wen of the Globe staff contributed to this report. Chelsea ­Conaboy can be reached at ­cconaboy@boston.com. Follow her on Twitter @cconaboy. Peter Schworm can be reached at pschworm@globe.com.